We've been improving the explanation in the soon-to-be-released new version of LF. Here is the relevant bit:
For the [Require Export] to work, Coq needs to be able to
find a compiled version of [Basics.v], called [Basics.vo], in a directory
associated with the prefix [LF]. This file is analogous to the [.class]
files compiled from [.java] source files and the [.o] files compiled from
[.c] files.
First create a file named [_CoqProject] containing the following line
(if you obtained the whole volume "Logical Foundations" as a single
archive, a [_CoqProject] should already exist and you can skip this step):
[-Q . LF]
This maps the current directory ("[.]", which contains [Basics.v],
[Induction.v], etc.) to the prefix (or "logical directory") "[LF]".
PG and CoqIDE read [_CoqProject] automatically, so they know to where to
look for the file [Basics.vo] corresponding to the library [LF.Basics].
Once [_CoqProject] is thus created, there are various ways to build
[Basics.vo]:
- In Proof General: The compilation can be made to happen automatically
when you submit the [Require] line above to PG, by setting the emacs
variable [coq-compile-before-require] to [t].
- In CoqIDE: Open [Basics.v]; then, in the "Compile" menu, click
on "Compile Buffer".
- From the command line: Generate a [Makefile] using the [coq_makefile]
utility, that comes installed with Coq (if you obtained the whole
volume as a single archive, a [Makefile] should already exist
and you can skip this step):
[coq_makefile -f _CoqProject *.v -o Makefile]
Note: You should rerun that command whenever you add or remove Coq files
to the directory.
Then you can compile [Basics.v] by running [make] with the corresponding
[.vo] file as a target:
[make Basics.vo]
All files in the directory can be compiled by giving no arguments:
[make]
Under the hood, [make] uses the Coq compiler, [coqc]. You can also
run [coqc] directly:
[coqc -Q . LF Basics.v]
But [make] also calculates dependencies between source files to compile
them in the right order, so [make] should generally be prefered over
explicit [coqc].
If you have trouble (e.g., if you get complaints about missing
identifiers later in the file), it may be because the "load path"
for Coq is not set up correctly. The [Print LoadPath.] command
may be helpful in sorting out such issues.
In particular, if you see a message like
[Compiled library Foo makes inconsistent assumptions over
library Bar]
check whether you have multiple installations of Coq on your machine.
It may be that commands (like [coqc]) that you execute in a terminal
window are getting a different version of Coq than commands executed by
Proof General or CoqIDE.
- Another common reason is that the library [Bar] was modified and
recompiled without also recompiling [Foo] which depends on it. Recompile
[Foo], or everything if too many files are affected. (Using the third
solution above: [make clean; make].)
One more tip for CoqIDE users: If you see messages like [Error:
Unable to locate library Basics], a likely reason is
inconsistencies between compiling things _within CoqIDE_ vs _using
[coqc] from the command line_. This typically happens when there
are two incompatible versions of [coqc] installed on your
system (one associated with CoqIDE, and one associated with [coqc]
from the terminal). The workaround for this situation is
compiling using CoqIDE only (i.e. choosing "make" from the menu),
and avoiding using [coqc] directly at all. *)
